The elastase model of emphysema in the guinea pig results in pathology resembling panacinar emphysema seen in frequently humans. We propose to use both proton and helium MRI to follow, in vivo, the development of emphysema in this model from the earliest to the latest stages of the disease. Proton imaging will allow us to define the interstitial changes and hyperpolarized helium will provide data on the expected changes in the distal air spaces. We will combine these structural analyses with assessments of pulmonary function to clarify the physiologic interpretation of the MR images.